Interconnection devices

ABSTRACT

A spring system arrangement and a related connector are disclosed. The purpose is to allow the use of contact springs, such as coil contact springs, with relatively large size body, to be located on a small center distance, i.e. pitch, and to electrically connect with contact pads of high density electronic devices, having a small device pitch. The device pitch can be smaller than the diameter of the spring body itself. In order to achieve this desired small spring pitch and high density, the contact springs are located in a nested head-to-toe and/or staggered orientation. Furthermore, the connectors utilize guide plates, referred to as combs, to accurately control the alignment of the contact springs tips to the contact pads of the electronic devices.

REFERENCE TO RELATED APPLICATION

This application is a utility application claiming the priority andbenefits of three provisional applications; 1) Ser. No. 60/231,387,filed Sep. 8, 2000, entitled Probers, and 2) Ser. No. 60/257,673, filedDec. 22, 2000, entitled Probes and Sockets, and 3) Ser. No. 60/268,467,filed Feb. 12, 2001, entitled Probes, Sockets, Packages & Columns; allof which are incorporated herein in their entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to electrical connectors, andmore particularly relates to high-density electrical connectors used intest and burn-in done on miniaturized electrical components.

This invention is a technology platform that enables the interconnectionbetween high-density electronic devices. It covers the springs andsprings arrangements that represent the modular building block ofdevices to achieve high density interconnection.

2. Background Information

It is standard procedure to test chips or integrated circuits atdifferent production stages to cull out the defective ones. Such testsare often done on printed circuit boards circuits, substrates andsimilar electronic devices as well. This is done to avoid putting extratime, money and effort into a defective component only to end up havingto scrap the component at the end of the production process.

In addition, sockets and connectors are used to mount electronicpackages and devices onto substrates, instead of soldering them directlyonto those substrates. These connectors and sockets need to have theircontact springs located on small center distance, which is usuallyreferred to as pitch, so as to match the pitch of those devices, whichare usually referred to as High-Density devices.

3. Prior Art

There exist a number of prior art devices of the type in considerationherein. I will explain in the following paragraphs how each of theseprior art devices have addressed some of the problems, but left someother issues unanswered and unresolved. I will explain how my presentinvention addresses and solves these issues.

1. Force-Deflection Curve and Damage to the Device Contacted by theSprings.

A potential user of my devices complained that his present supplierprovides him with test heads, which utilize contact springs similar tothe IBM Buckling Beam contact springs. He stated to me that the springsapply such a high force that sometimes they damage the substrate thatare tested. So, they start with potentially good substrates, test themand during the test process, the substrates get damaged and becomedefective. It is almost like testing matchsticks. After each one getstested, you determine that it “was” a good one.

In U.S. Pat. No. 4,622,514, the IBM “Multiple Mode Buckling Beam ProbeAssembly”, the contact springs are basically straight columns of wires,which get compressed by an external force to provide the contactpressure and contact force. There are basically two reasons why anyelectrical interconnection device needs springs and needs forces appliedon to these springs. The first reason is to break through the layers ofdirt and oxides that form on the contact surfaces and to reach the purecontact metal. In some cases the required force is only a few grams, inother cases it can be considerably higher. The second reason is toaccommodate non-planarity of the contacts on the surface of the deviceto be contacted. For example, if the device has a non-planarity of sayseveral thousands of an inch between any two adjacent contact pads, thenone spring would have this much more deflection than the adjacentspring. The effect of this additional deflection is that the spring withmore deflection will exert more force on the contact pad. This higherforce could reach a level, where the contact spring would then damagethe contact pad and render it defective.

So, in order to prevent any damages to the contact pads, the contactforces need to be kept within tight limits. For this reason, it iscustomary to select contact springs that are “soft” and have a shallow“force-deflection” curve, also called “spring index”. With a softspring, you start by applying a small force and gently, graduallyincrease the force until you reach the desired force level that isenough to break through the layers. Ideally you should stop there. Ifthe device was perfectly flat and the non-planarity was zero, then allthe springs should have the same deflection and thus the same contactforce. But if one contact pad is lower than the others, then the springtouching this pad would not have been deflected as much as the othersprings, consequently the force provided by this spring would be smallerthan the force provided by the other springs. So, the force on that lowpad would be below the desired level. In order to make this force higherand to make it reach the desired level, the spring working on this lowpad needs to be deflected more.

But we cannot selectively deflect each individual spring on its own. Allthe springs have to be pushed down and deflected equally, by the sameamount. So, we push down on all the springs, until the spring acting onthe lowest pad reaches a deflection that would provide the desiredforce. But the springs acting on the higher pads, because of theirlarger deflection, are now providing a much higher force. The amount ofthis additional force can be calculated from the force-deflection curve,or the stiffness of the spring.

If the springs used are relatively stiff, this can have a detrimentaleffect. The excessive down-push on the springs can make the force of thehigh pads reach a level, where the pads can be damaged. A secondary badeffect of this situation is the total force required to be applied onthe device. If we have a device that has a high number of contact pads,and the force per pad to reach a satisfactory electrical connection, thetotal mechanical force can damage the device physically. For all theabove reasons, designers put a lot of effort in designing soft contactsprings. The ideal spring would have a force-deflection curve thatstarts at zero force for zero deflection and then slopes upwardgradually.

Now, if we look at the force-deflection curve of a column, unfortunatelyit has the opposite shape, or general slope, compared with thedesirable/ideal springs. A column stays straight under an increasingforce and when the force reaches a critical level, the column bucklesand gives way very rapidly. If we study the force-deflection curve of acolumn, we will see that basically it has a shape and slope contrary tothe ideal contact spring. At the beginning, when a force is applied to acolumn, we see no deflection. Even after increasing the force to a highlevel, there would still be no deflection. The force-deflection curve ispractically a straight vertical line with zero deflection. After theforce reaches the buckling level or limit, the column buckles andpractically collapses down. The force-deflection curve drops down almostexponentially until it reaches a point where the structure converts to abeam mode under axial loading. The slope of the curve after the initialbuckling usually becomes negative. Such a condition is not desirable,especially with any appreciable non-planarity. To reduce thisundesirable effect, IBM has opted to provide several steps of buckling,to accommodate more non-planarity than is available with one level. But,in spite of that, the basic force-deflection curve is the same. The onlydifference is that with the multi-level buckling, we would get a curvethat would look like a saw tooth. The force would increase to thebuckling limit then collapse at the first buckling, then the force wouldincrease again to a similar buckling level and then collapse at thesecond buckling and so on.

The contact springs according to the present invention provide the moredesirable force-deflection curves as will be describes later. This meansthat they would not have the tendency of damaging the contact pads ofthe device under test.

In U.S. Pat. No. 5,385,477, the CK Technology “Contactor with ElastomerEncapsulated Probes” has modified the design of the IBM Buckling Beamslightly. Instead of relying only on the applied force to buckle thebeam, CKT has provided means to “nudge” the column to collapse moreeasily. However, the force-deflection curve is still basically that of acolumn and it would have a similar vertical spike, for one columnsegment, and if more than one segment, then the saw tooth shape, asdescribed above. Hence, no drastic improvement.

As mentioned above, the contact springs according to the presentinvention provide the more desirable force-deflection curves as will bedescribes later. And again, this means that they would not have thetendency of damaging the contact pads of the device under test.

2. High-Density or Small Pitch.

All the patents listed below in this section have been invented by thepresent inventor, Gabe Cherian, either solely by him or together withother co-inventors. The reason for listing them is to show that each oneof them has one or more features which make them not compatible with thepresent needs of the industry, from the point of view high density. Thisis the reason the inventor was motivated to update his old inventionsand to address the present market needs.

G. B. Cherian, W. S. Scheingold and S. J. Kandybowski, “ElectricalInterconnect Device”, AMP Incorporated, Harrisburg, Pa., U.S. Pat. No.4,262,986, Apr. 21, 1981. Shows a large footprint compared to the height(excluding the soldertail). Totally opposite of what is being achievedin this invention.

G. B. Cherian, W. S. Scheingold and L. D. Wulf, “Zero Insertion ForceConnector”, AMP Incorporated, Harrisburg, Pa., U.S. Pat. No. 4,080,032,Mar. 21, 1978. Only 2 rows of contacts, then we can use the spacebetween the rows or outside the rows.

E. J. Bright, G. B. Cherian and W. S. Scheingold, “Ejection Device for aElectronic Package Connector”, AMP Incorporated, Harrisburg, Pa., U.S.Pat. No. 4,190,310, Feb. 26, 1980. Same. Only 2 rows of contacts, thenwe can use the space between the rows or outside the rows.

G. B. Cherian, W. S. Scheingold and F. C. Youngfleish, “Active DeviceSubstrate Connector”, AMP Incorporated, Harrisburg, Pa., U.S. Pat. No.4,341,433, Jul. 27, 1982. Perimeter. Almost like the 2 rows, except atthe corners. 2 rows or perimeter: Worry about the center distance onlyin one direction, but have more room in the direction perpendicular tothe former.

G. B. Cherian, W. S. Scheingold, “Connecting Element for Surface ToSurface Connectors”, AMP Incorporated, Harrisburg, Pa., U.S. Pat. No.4,161,346, Jul. 17, 1979. Close but too difficult for real small pitch

G. B. Cherian, W. S. Scheingold and R. D. Zimmeran, “ElectricalInterconnection Device”, AMP Incorporated, Harrisburg, Pa., U.S. Pat.No. 4,199,209, Apr. 22, 1980. Close but too difficult for real smallpitch

Cherian, Gabe, “Heat Recoverable Connecting Device”, RaychemCorporation, Menlo Park, Calif., U.S. Pat. No. 4,487,465, Dec. 11, 1984. . . . Close but too difficult for real small pitch.

The IBM “COBRA” has one advantage over the Buckling Beam, but it has amajor drawback. It can not be parallel nested close enough toaccommodate high-density in both the x- and the y-directions. FIG. 12.Ashows the general configuration of the IBM Cobra Spring or Needle. If weplace such springs next to each other, but without allowing them totouch, in a direction perpendicular to the plane of the belly, which wewould arbitrarily call the y-direction, the center distance between anytwo adjacent springs would depend on the diameter of the spring. Forexample, if we want the clearance between any two adjacent springs to beequal to one diameter of the springs, then the center distance would beequal to two diameters. But on the other hand, if we try to parallelnest two or more such springs, in the direction shown in FIG. 12A, whichwould be in this case the x-direction, the center distance will beconsiderably larger. The reason is because the C-Shape belly of the IBMCobra Springs is almost a half circle. In order to prevent the springsfrom touching, and thus shorting electrically, and have a similarclearance of one diameter between any two adjacent springs, as in theprevious case, the springs will have to be placed at a much largercenter distance.

In the present invention, we present ways to decrease the centerdistances between springs, thus accommodating higher densities ofcontacts pads.

3. Impedance Control

In all the above prior art, the contact springs are bare, i.e. notcovered by any insulation or the like. If the spring is long, then itslength may affect the quality of the electrical transmission. In thepresent invention, we present ways to control the impedance of thecontact springs and improve their electrical performance.

4. Wipe or Scrub

In all the above prior art, as well as in the Charles Everett “POGO”pins and all similar contact springs, the tips of the springs apply theforce at one point of the contact pad. They do not provide “wipe” or“scrub”. If a contact spring provides wipe or scrub, it help in removingthe undesirable layers of dirt and/or oxides from the space under thespring and allows the spring to make metal contact under a smallerforce, than when there is no wipe or scrub. So, all the prior artmentioned above, by not providing wipe or scrub, require a comparativelyhigh force to make a good electrical connection, compared with a contactspring that does provide the desirable wipe or scrub. The presentinvention does provide means to have wipe or scrub as will be describeslater.

5. TCE Matching

In all the above art and in most sockets or connectors, the springs arelocated in housings, usually made of plastic. Then the sockets orconnectors are mounted on boards, which are usually made of FR4 orglass-filled epoxy material or the like. Then the device under test, forexample, a BGA package is placed on top of the socket or connector, andthe whole stack would be placed in a thermal cycling oven. The TCE(Thermal Coefficient of Expansion) of these material can varydramatically. During thermal cycling, these different materials wouldexpand and shrink at different rates. The effect of this can bedetrimental, especially for large temperature variations, and for thematerials in contact with each other. There would be a “relative motion”between the tips of the springs and the contact pads, both at thesocket/board interface, as well as at the socket/package interface.

The present invention covers improvements to this undesirable conditionas will be explained later.

6. Elastomer with Dispersed V Springs

U.S. Pat. No. 4,660,165, for the Shin-Etsu “Press-Contact TypeInterconnectors” rely on the elastomer to provide some of the contactforce. This is not what I am doing here in my invention. Wherever I usean elastomer, it is simply as a means to hold the springs together tofacilitate the assembly process. As I have explained in the description,I can use a wax to hold the springs together and after the assembly isdone, I can melt the wax away and the socket would work just as wellwithout the wax or the elastomer.

REFERENCES

-   1. J. Novitsky and C. Miller, “MicroSpring™ Contacts on Silicon:    Delivering Moore's Law-type Scaling to Semiconductor Package, Test    and Assembly”, FormFactor Inc., Livermore, Calif., International    Conference on High Density Interconnect and Systems Packaging,    Denver, Colo., Apr. 25-28, 2000, Proceedings pp. 250-255.-   2. Novitsky, John, “Production Sockets Using MicroSpring™ Contacts”,    FormFactor Inc., Livermore, Calif., International Conference on High    Density Interconnect and Systems Packaging, Denver, Colo., Apr.    25-28, 2000, Proceedings pp. 363-368.

PRIOR ART

Pogo pins and similar springs are used frequently to connect to and totest electronic packages and devices. However, Pogo pins usually havefairly large diameters compared to the small pitch of many newHigh-Density devices. If Pogo pins and springs are “miniaturized”, sothey would accommodate these High-Density devices, they become ratherexpensive. The purpose of the present invention is to use the ratherless expensive large diameter Pogo pins and springs and yet stillaccommodate those High-Density packages and devices.

SUMMARY OF THE INVENTION

As the electronics industry has become more advanced, the chips andcomponents have become smaller and smaller. A resulting problem is thatsockets, probes and the like are too large, or have their contactelements too large, to work with many of the products which are nowavailable. This results in increased cost to the manufacturers, who musttest the devices through more expensive means.

The object of the invention is to utilize new systems to design andmount springs or needles to reduce the drawbacks that exist in presentprobes and sockets. This method can be used for probes, sockets, testheads and other interconnections. The basic goal is to provide contactsprings that can be located on small, effective center distances tocorrespond to the center distances of contact pads on chips, wafers,packages, substrates or boards and similar devices. This should alsocover a small area or footprint of the devices.

Still other objects and advantages of the present invention will becomereadily apparent to those skilled in this art from the followingdetailed description wherein I have shown and described only thepreferred embodiments of the invention, simply by way of illustration ofthe best modes contemplated by carrying out my invention. As will berealized, the invention is capable of modification in various obviousrespects all without departing from the invention. Accordingly, thedrawings and description of the preferred embodiment are to be regardedas illustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 through 8 show the basis of the invention, what I like to callthe basic technology.

FIG. 1 shows the basic contact element and how it is formed to act as“formed beam” rather than a “column”. It interacts with what I call thecomb. The tail of the spring passes through an aperture in the comb,said aperture acts in turn as a fulcrum for the tilting of the springtail.

FIG. 2 shows a cantilever beam, which has similar features. Its tailpasses through an aperture of a comb, which in turn controls the tiltingof the spring tail as well.

FIGS. 3 and 4 show how springs can be “parallel nested”.

FIGS. 5 through 7 show how springs can be placed in a “Nested Staggered”arrangement.

FIG. 5 shows an arrangement as per present invention, which would resultin a reduction of the center distance or pitch (42) between the tips ofthe contact springs.

FIG. 6 shows a top view of one corner of the arrangement shown in FIG.5. It shows the small diameter of the pushers and the larger diameter ofthe body of the springs. It rather shows their “footprints”. This figureshows very clearly and highlights the “Nesting” effect. It shows thefact that each spring encroaches on the footprint of the springsadjacent to it, but this applies only to the “footprints” of thesprings. It shows that the bodies of the springs would interfere witheach other, IF the bodies were all at the same height or elevation orare at the same level. But comparing this FIG. 6 with FIG. 5, it becomesobvious that the bodies do NOT interfere, because they are at differentelevations/levels.

FIG. 7 shows a 3-D view of a matrix of such springs. It shows thedifferent slabs 105, 106, etc. And how the springs at one row elevation,say the top level, are staggered with respect to the springs in the rowthat is at the other elevation, i.e. the bottom level in this case. Italso shows how the springs are encroaching on the “envelope space” or“footprint” of their adjacent springs. Furthermore, FIG. 7 shows how thevarious slabs, e.g. slab 105, 106, etc. are also similarly staggered andnested, within themselves, as well.

FIG. 8 shows how springs can be placed in a “Head-To-Toe” arrangement.

FIGS. 9 through 47 show applications of parallel nesting. These apply tointerconnection devices, usually known as “sockets”.

FIGS. 48 through 68 show similar applications of parallel nesting, butthe applications are for interconnection devices, generally known as“probes”, test heads, test modules, and the like. All contact springs inFIGS. 9 through 68 could be considered to have “vertical axis”.

FIGS. 69 through 101 show applications of cantilever type of springs, asthey are used in applications which also use the “combs”. Theseapplications are usually known as “probes” or “probe cards”. Some willbe referred to as “horizontal cantilever”, while others as “verticalcantilever”, based on whether the anchor portion of the springs ishorizontal or vertical respectively.

FIG. 102 is the drawing, which will be attached to the “abstract”. Itshows a socket, which is designed according to the teachings of thisinvention.

DEFINITIONS

For the purpose of the following invention description, I will usecertain words or terms that may be peculiar to this application. Theywill be explained in the following definitions. For different springelements and portions, please refer to the various figures in thisSpecification.

Definitions

Pitch or Center Distance. Distance between the Center of a contactelement, e.g. spring, and the Center of an adjacent contact element,usually in line, or in a row containing two or more such contactelements. This center distance is usually referred to also as “pitch”.

Spring Tip or simply the Tip. The farthest point of a spring, whichgenerally makes contact to a device, such an electronic chip or packageor substrate or board. Most springs would have two active tips, whilesome springs could be fixed at one end, in which case they would haveonly one tip active, which is the tip that is not fixed.

Spring Body or simply the Body. It is the major part of the spring,between the two tips or between the one active tip and the fixed portionof the spring.

Spring Footprint or simply Footprint 36 in FIG. 6. If a spring islocated so as to make contact with an electrical device, such as asubstrate or printed circuit board, and if we look at the area of boardsurface that the spring occupies or shadows, we will refer to that areaas the spring's footprint on the board, or simply its “footprint” 36,FIG. 6.

Nesting. When we place two objects adjacent to each other, and oneobject encroaches on the “envelop space” or “footprint” of the adjacentobject, we can say that the object is nested into the other one. If theobjects are similar in shape and orientation and are parallel to eachother, then we can further define such nesting as a “parallel nesting”.

Envelope Space, or synonymously simply Envelope or simply Space. If weget a sheet of shrink Seran Wrap and wrap it over and around any objectand shrink it, then it will define a space, which I would like to referto as the “Envelop Space” of the object. For example, if we take a dishof plate or salad bowl and cover its top by a sheet of Seran Wrap toenclose the contents of that container, then the Seran Wrap sheet woulddefine the top envelop space of that container. If we try to “nest” asecond container in the above one, we will not be able to do so, unlessthe second container breaks through the Seran Wrap sheet. If thishappens, then we would say that the second container has encroached onor into the envelope space of the first one.

Parallel Nesting. Plastic spoons and forks used for picnics and the likecome packaged in cardboard boxes, stacked neatly one next to each other.They can be considered as elongated slender objects, which are “parallelnested”. Plastic or paper cups stacked one inside the other, or dishesstacked one on top of the other, or some metal chairs stacked one on topof the other are examples of parallel nesting. All these and similarobjects, which can be arranged such that one object “encroaches” on thespace of the adjacent object, can be considered as being “parallelnested”. The main purpose of parallel nesting in these cases is to useless space to contain such objects, compared with the space required ifthese objects were placed next to each other or on top of each other,whereby each one occupies its own space, without encroaching on thespace of the adjacent object. So, for the purpose of this invention, wewill define “parallel nesting” as placing objects adjacent and parallelto each other, in such a way that one object is encroaching into the“space” of the adjacent object, and such that the space utilized by anytwo adjacent objects is smaller than the total space that would havebeen used by the two objects if they were not encroaching on eachother's space. The same would apply to objects encroaching on eachother's “footprint”. They would also be considered to be parallelnested. Parallel nested objects can be touching their adjacentneighbors, or they can be placed at some predetermined distance, and canstill be considered parallel nested, if they encroach on the space orfootprint of their respective adjacent object(s). The same applies tocontact springs. They can be parallel nested and kept at a certaindistance from each other. We may refer to that distance as the “centerdistance” between the springs or the “pitch”.

Non-Parallel Nesting. Another way of nesting is shown in FIGS. 5, 6, and7. In these cases, the individual parts do have similar shapes, but theyare juxtaposed in an inverse, up-side-down position, which I refer to as“head-to-toe” arrangement. In addition, the parts do encroach on eachother's “envelope space” or on each other's footprints, as seen in allthese figures, but as seen especially clearly in FIG. 6. I will refer tosuch an arrangement as “Non-Parallel Nested Head-to-Toe” or simply as“Nested Head-to-Toe”.

Row. FIG. 5 shows two rows of springs, 95A and 95B. In this FIG. 5, thetop row 95A has 8 springs and the bottom row 95B has 9.

Slab. FIG. 7 shows a number of slabs, stacked one behind the other. Thefirst slab, within plane 105, consists of 2 rows, as defined above andas shown in FIG. 5. In this FIG. 7, this first slab 105 has a total of17 springs. Each slab will be identified by its plane. So, the firstslab will be referred to as slab 105, the second slab will be 106, etc.

Matrix. When we place a number of slabs next to each other, we couldrefer to them as a matrix. FIG. 7 shows a matrix of 17 slabs.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the invention is susceptible of various modifications andalternative constructions, certain illustrated embodiments thereof havebeen shown in the drawings and will be described below in detail. Itshould be understood, however, that there is no intention to limit theinvention to the specific form disclosed, but, on the contrary, theinvention is to cover all modifications, alternative constructions, andequivalents falling within the spirit and scope of the invention asdefined in the claims.

While I am describing the drawing in more details, I will at the sametime explain the technology basis of the invention. I will also includea number of examples in this section, which should be considered as partof the embodiments for the purpose of this application as well. Theembodiments in the section on “PREFERRED EMBODIMENT” are additionalones.

This description covers more than one invention. The inventions arebased partly on the same technology platform, but then each of theinventions has some additional features of its own. Not being an expertin handling patents, I would like to leave it to the patent examiner todecide on the number of the inventions contained and how to split oneinvention from the other.

I will also cover in this application a number of embodiments for someof the described inventions. Some will relate to the springsarrangements, others will relate to the springs themselves, while otherswill relate to combs. Moreover I will cover embodiments of applicationsutilizing the said springs, their arrangements and the combs and thenexpand with additional features.

I will first describe the basic technology platform that is common toall the applications. I will use some socket embodiments to illustratethe technology. Then I will describe other socket embodiments on theirown.

I will then describe each of the other applications separately.

Finally, I will describe some new features that are common to manyapplications.

Moreover, I will describe some additional features, related to someindividual applications. These new features are not based on the commonbasic technology that I started with at the beginning.

(Section 1—Technology & Sockets)

A. “Staggered” and “Head-To-Toe” Springs Arrangement

Summary of the Concept

Frequently, contact springs have shapes where one part of the spring islarge, while other parts are smaller.

For example, in FIG. 5 a compression coil spring 82L or 82R, with acylindrical body, has a coil 84A or 84B with a large outside diameter,while the end rod 86 or 88, referred to as pusher or tip, is muchsmaller in diameter. In other cases the spring body itself is tapered,such that one end is larger in diameter or girth than the other end; orhas a double taper, where the middle is larger than the ends.

Conventional “In-Line” Arrangement, referred to as “CONVENTIONALShoulder-to-Shoulder” or as “CONVENTIONAL Head-to-Head”.

The conventional arrangement is to place the springs side by side insidepockets of the housing. See top row 95A or bottom row 95B in FIG. 5. Allthe pockets are at the same height or at the same elevation and thesprings are consequently placed also at the same elevation, i.e. side byside. I would refer to such an arrangement as the “In-Line” arrangementor as “CONVENTIONAL Shoulder-to-Shoulder” or as “CONVENTIONALHead-to-Head”, because this is the conventional arrangement. Thiscreates a matrix of springs inside a matrix of pockets, all in onehorizontal row at the same height or level or elevation. The pitch, 43in FIGS. 5 through 7, or 43A or 43B in FIG. 5 ???, which is the distancebetween the centers of the springs in this one row will be equal to thelargest diameter or girth of the spring, plus the wall thicknessseparating the pockets from each other plus the clearance that is neededbetween the pocket and the spring, to allow for free movement of thesprings.

“Staggered” Springs Arrangement, or “Head-to-Toe”

FIG. 5 shows what I would like to refer to as “nested staggered” springsarrangement. The springs 82L and 82R are arranged such that they wouldhave the large portion 84L or 84R of the body of one spring located nextto a smaller portion 86 or 88 of the body of the adjacent spring. Theywould also be placed in two horizontal rows 95A or 95B, at two differentlevels or heights, with the springs of one row offset horizontally by,i.e. moved sideways by, one half 42, of a conventional pitch 43 withrespect to the other row, as in FIG. 5. Hence the term “nestedstaggered”. They would be nested, in the sense that the footprint of onespring would encroach on the footprint of the adjacent spring, as shownin FIGS. 5 through 7. This is in contrast with the conventionalarrangement, where all the springs are arranged such that the largestportion 84A of each spring is next to the corresponding largest portion84A of the adjacent spring, which I referred to as “In-Line” or“shoulder-to-shoulder” or “head-to-head” or rather as “conventionalshoulder-to-shoulder” or “conventional head-to-head”. Thus the centerdistance 42 between the adjacent springs in the “staggered” or“head-to-toe” arrangement will be smaller than the center distance 43 inthe case of the conventional “In-Line” or “shoulder-to-shoulder”arrangement.

Preferred Embodiment

FIG. 5 shows an example of a “socket” or “connector” 91 built andassembled according to the concepts and manufacturing and arrangementsmethods covered here, specifically using the staggered nestedhead-to-toe spring arrangement.

The contact springs 82L and 82R are located inside a socket 91. Thesocket 91 includes the upper and lower “combs” 93A or 93B and thehousing body 92. Depending on the application, the socket may also havea lid to push down

on the device under test (DUT), a latch to hold the lid down, and otherperipheral components.

FIG. 7 shows an isometric view of the springs shown in FIG. 5, butwithout the housing, for clarity's purpose.

Let us also agree on the coordinate directions. If we look at the socketor the spring matrix from the top, then we will say that this is the x-and y-directions 101 and 102, as in FIGS. 6 and 7 If we look at the sideview, as in FIG. 5, then the horizontal direction is the x-direction101, while the vertical direction is the z-direction 103.

The 3-Dimensional view in FIG. 7 shows all three directions.

FIG. 6 shows a top view of a portion of the socket; thus it is showingthe x- and y-directions 101 and 102.

The springs in the socket, which is shown in FIGS. 5 through 7, andwhich is according to the present invention, are arranged in a way,whereby the large portion of any spring is located next to the smallerportion of all the springs adjacent to it. The springs are placed in two(or more) rows 95A or 95B, staggered and offset horizontally. Thepushers 86 or 88 are elongated enough to reach their respective contactpads. The basic concept is to stagger and/or offset the contact springs,thus reducing the “effective” pitch.

The top row 95A is offset sideways, in the x-direction 101, by adistance equal to half the CONVENTIONAL pitch with respect to the lowerrow 95B, and the pushers 86 or 88 of the contact springs 82L or 82R areextended to reach both the top and bottom surfaces of the socket 91, asshown in FIG. 5. The pushers 86 or 88 will then protrude further beyondthe combs 93A and 93B, to make contact with the devices, not shown, thatwill be contacted by the springs. These pushers are now practically atalmost twice the density of the conventional method, in each of the xand y directions.

Note that the top row 95A together with the bottom row 95B constitute aslab, as per Definition. In this case, it is slab 105.

Now Some More Details

FIG. 5 shows a cross-sectional side view of the “nested staggered”arrangement. This method applies to coil springs, “Pogo” pins and othersimilar springs, where the spring has a relatively large size body and arelatively small size “tip” or “pusher”.

FIG. 7 shows a 3-Dimensional view of the springs. The housing has beenremoved simply to be able to better see how the springs are arranged.The first slab 105 has been described earlier. The second slab 106 wouldbe similar to the first slab 105, but turned up side down, so that theadjacent springs in the x and y-direction would also be staggered andarranged in a Nested Head-to-Toe arrangement, with respect to the firstslab 105. The third slab 107 will be arranged like the first 105, andthe fourth slab 108 will be arranged like the second 106, etc. In otherwords, all odd numbered slabs, in the y-direction 102, would look alikeand all even numbered slabs would look alike.

FIG. 6 shows a portion of an enlarged top view of the above socket orconnector. It shows the improvement in density. The size of theresulting pitch 42 is almost one half of the size of the conventionalpitch 43, depending on the ratio between the diameters of the body andof the pushers. It also shows how the footprint 36 of one spring looksas if it is encroaching on the footprint 36 of the adjacent springs.This is simply an illusion. We know better now. Since the springs arestaggered in the elevation and nested as described above, they do notphysically interfere with one another.

There are, however, some limitations or disadvantages to thisarrangement of pins or springs. First, the total height of the socketwill be increased. For testing and burn-in, this should not be a seriousproblem. Additionally, springs could be made fatter and shorter reducingthe overall height. Second, the total path for the electric signal willbe longer. This creates additional electrical path length, andadditional inductance and/or impedance. The electrical path can beshortened by plating the inside surfaces of the pockets 94A and 94B,thus reducing the effective electrical path length. Creating electricalpaths that can be provided inside the barrier walls, between thepockets, and that do not touch the insides of the pockets may achieveadditional improvements. This could then be electrically connected toground, acting as an electrical barrier or shield against strayelectrical signals or noise.

“Head-To-Toe” Spring Arrangement

The “head-to-toe” arrangement, according to the present invention isillustrated in FIG. 8.

In some cases, the spring main body shape or “envelope” may look morelike a triangle, as in FIG. 8, or a trapezoid or diamond-shape, wherethe body is wider at one point than at another point, but where the pushrods are still thinner than the general main body. In such a case, thesprings can still be arranged in a staggered form as above, but we canbenefit even more from their peculiar shape and arrange them, as in FIG.8. I refer to this as the “Staggered Head-To-Toe”, or simply the“Head-To-Toe” arrangement.

This arrangement would not only reduce the center distance between thesprings, but will also reduce the total height of the whole arrangement.

1. B. “Parallel Nesting” Spring Arrangement

Summary of the Concept

An alternate approach is to use parallel nested springs. The parallelnesting arrangement utilizes springs that are formed such that they canbe arranged side by side at close proximity and can be nested into eachother, thus occupying less space than if they were not nested insideeach other.

The concept of parallel nesting is really not new. What is new isapplying the concept to contact springs in the context of thisinvention/application.

The concept is similar to the following very obvious examples. When westack dishes in a cupboard, in essence we parallel nest them. When wehave a stack of paper or plastic cups that are shaped to suit thepurpose, we are parallel nesting them. When we stack metal chairs on topof each other, again, we parallel nest them. Plastic forks or spoonsthat are sold in small container would take a much larger space, if theywere not parallel nested.

In all these examples, if we did not nest the objects “inside” eachother, they would occupy a larger space. Looking at it in a differentway, we can say that the (center) distance between any two adjacentobjects is much smaller if they were parallel nested, than if theobjects were placed side by side without nesting, or if they were simplythrown in next to each other at random.

The above, then, will be our definition of “parallel nesting”. (See alsothe “DEFINITION” section. The concept of this invention is basically anextension of the idea of parallel nesting, applying it to springs thatcan be used to connect electrical devices. In addition, the inventionintroduces other features, as will be explained below.

Each spring constructed in accordance with the present invention isshaped such that it can be parallel nested, so as to occupy a smallereffective space, than if the springs could not be parallel nested.

An additional, optional, feature of a spring constructed in accordancewith the present invention, is that the spring would be basically aslender column that has one or more portions of its length offseteccentrically away from the spring axis, to ensure that the deflectionunder external forces will occur in a gentle and predictable fashion.

The springs can be wire formed or stamped. The springs can be shapedlike a “C” or a “Chevron” or a variety of shapes as will be shown later.They would have a “belly” that protrudes usually beyond their effective“pitch” and encroach on the footprint of the adjacent spring. However,since all the springs are parallel and nested in the same direction,they would not touch.

Please notice also that these are “discrete” springs, each one“addressing” a particular contact point on the DUT. This is in contrastto some “random” distribution of springs inside a carrying layer ofelastomeric material or the like.

Illustration Example

FIG. 9 is an illustration of parallel nested springs. In this case, thesprings are “C”-shaped. They are shown under No-Load, i.e. with nodeflection.

FIG. 10 shows the same springs, but under some load. The naturaltendency of such springs, when compressed by an axial load, is to deformas shown. Their bellies have bulged, but because they are all paralleland nested in the same direction, they still do not touch. The tails ofthe springs tilt when compressed, as shown. Please notice the somewhatslanted hourglass shape of the holes in the top and bottom combs. Thisshape does not “fight” the natural tendency of the springs tails torotate or tilt.

Wipe or Scrub

Assuming that the device under test (DUT) to be contacted by thesesprings is “fixed” horizontally or “guided” with respect to the combs,then the compression of the springs creates a horizontal relative motionbetween the spring tips and the contact pads of the DUT. This relativemotion creates a “wiping” or “scrubbing” action. This is very desirable.(See also the “DEFINITIONS” section).

The wipe or scrub is almost like “plowing” through dirt. It helps toremove or scrape off and to penetrate through the layers of oxides thatform on the contact surfaces of DUTs, and to expose the base metal. Thispromotes good electrical contact. Wipe or scrub exposes the base metaland allows the contact spring to make good electrical contact to thatbase metal, using a smaller contact force than if we do not have suchwipe or scrub.

We will talk more about wipe and scrub, when we describe the “probes”.

APPLICATION EXAMPLE 2

FIGS. 11 and 12 show a socket implementation containing a matrix of 20by 20 “C” springs. We are looking at a side view in the x-z directions.This shows only one row of 20 springs. The other rows are behind and arehidden.

FIGS. 21 through 24 and 30 and 31 show the top view of similar sockets,showing the full matrix.

FIGS. 21 and 31 shows the top view of the socket, with the 20 rows, eachhaving 20 springs.

The springs are shown in a “parallel nesting” arrangement, held in placewith two combs. We also see a middle member.

The middle member in FIGS. 11 and 12, called a “slider”, moves back andforth with the movement of the bellies of the springs. The springs canslide and move freely through the holes of the slider, as well asthrough the holes of the top and bottom combs.

The slider has a number of functions. First, it keeps the springs“organized”. Second, it helps to prevent the springs from touching eachother and “shorting. Third, it has another function, which will bedescribed later in conjunction with the “retracting springs”, which willbe described later in connection with FIGS. 32 through 35.

In this FIG. 11, the springs are under no-load. The tips of the springsare shown protruding beyond (above and below) the respective combs.

In a typical application the socket would be mounted on top of aload/test board, with the DUT on top of the socket, held in place with atop pressure means applying force on top of the package against thesocket springs. The springs would compress as they contact the DUT andthe test board.

Other Embodiment Examples

FIG. 13 shows another shape of springs that can be used to makehigh-density sockets. I refer to this shape as the “chevron” springs.These springs can be “stamped” or “wire formed” and are obviously“parallel nested”.

Under compression, we notice two things. First, the belly of the springsprotrudes to the side and the tips of the springs move sideways tocreate a desirable wiping action.

In FIG. 14 an individual “chevron” spring is analyzed in detail as itdeforms under an applied force. In order to see clearly what is goingon, I am showing only the centerline of the spring. As the spring isdeflected, the belly bulges from its “free” position (under No-Load orZero-Grams force) and moves to the left, while the tails of the springtilt. The tip of the spring, which will touch the DUT, moves inwards andsideways to the right.

The enlarged view shows the tip of the spring and the effect of springdeflection on the movement of the tip. The spring is in its comb thatcontrols the horizontal position of the spring. When the spring iscompressed inwards under the increasing load, its tip moves sideways,horizontally to the right, at the same time. This creates a desirable“wiping” action.

FIG. 15 shows stamped chevron springs on carrier strips. The figure onthe right-hand side shows some details of the tip. Please noticeespecially the tapered “barb” at about the end of the tail, just beforethe beginning of the shoulder. This would help in locating and retainingthe springs in a socket. It also has another benefit. It can create apre-load on the springs, so that we would need a smaller amount ofdeflection to reach the desirable contact force.

Spring Curves & Behavior

When the springs are loaded, by applying an external compressive forceon their tips, they would deflect. On one hand, they appear as if theywere columns buckling under a compressive force, but in reality, becauseof the preformed shape of the springs, they operate more as bent orformed beams under axial loads. The belly portions can be stressanalyzed as a beam, or as two cantilever beams attached together at thecenter of the spring.

The biggest benefit is that their force-deflection curves are usuallygentler than in the case of pure columns. See “Background” for adetailed description of the behavior of a column, as compared to aChevron spring that I will describe here.

The spring curve of a buckling beam in general is not desirable forelectrical contacts. See explanation in the “BACKGROUND” section.

A typical example of the force/deflection curve of a Chevron shapedspring is shown in FIG. 16. Notice that the curve starts at the origin,point 0,0. The curve rises at some steep slope for some amount ofdeflection, as for a slightly stiff spring. Then the slope graduallyflattens out and the springs behave like a softer spring. Theinteresting thing is that the curve is still rising, though at a smallerrate. The curve is continuous, and its slope is always positive.

FIG. 17 shows a typical curve for a “C”-shaped spring. It too has someflattening at the top of the curve, albeit not as pronounced as theChevron spring in FIG. 16.

In both these cases, the spring curve is desirable for electricalcontact springs.

Design Verification

In conjunction with Point Technologies, Inc., a manufacturer ofminiature springs and needles, we have made several springs of variousshapes and sizes, and tested them for the sockets and probesapplications.

The key points are:

Spring forces are available in a wide range.

Spring designs are able to obtain proper force deflection performance.

Wiping action is achievable and predictable.

Spring “Force-Deflection” Curves

I will describe the following two charts as typical examples of what canbe obtained in practical applications.

According to this invention, sockets can be designed with springs thatneed with contact forces that can vary from as low as 20-30 grams toover 250 grams. Probes can be designed with springs with smaller forcesdown to single digit grams.

FIG. 16 shows the Force-Deflection curve for a “Chevron” shaped spring(sample #2), made of Tungsten, with a wire diameter of 0.008″ (0.203mm). The flex portion was approx. 0.750″ (approx. 19 mm) tall, with abelly of approx. 0.100″ (approx. 2.5 mm). The total length was approx.0.375″ long (approx. 9.5 mm). The spring provides a force of over 50grams at a deflection of approx. 2.5 mm.

The non-linearity of the slope is very desirable. The curve has a steepslope at the beginning, and then its slope becomes shallower as thedeflection increases. The spring provides a high force at the beginningof the application as it starts to make contact with the package orsubstrate. This helps in breaking through the oxide layers, etc. Then,the force stabilizes, (does not change much for relatively largerdeflections), which compensates for any non-planarity of the package orsubstrate. This is very desirable, because it reduces the total forcerequired to hold down the DUT in the socket.

FIG. 17 shows the Force-Deflection curve for a “C” shaped spring. Thisis spring sample #6, also made of Tungsten, with a 0.008″ (0.203 mm)diameter. The flex portion was approx. 0.625″ (approx. 15.9 mm) tall,with a belly of approx. 0.150″ (approx. 3.8 mm). The total length wasapprox. 0.200″ long (approx. 1.9 mm). We can get approx. 37 grams forceat a deflection of approx. 1.8 mm. The total force of this spring is notmuch different than the Chevron spring but it is applied more linearly.

Materials

A number of materials are available to make the springs. They includethe following:

Beryllium-Copper (BeCu), which is used very frequently to make contactsprings.

Phos-Bronze, which is low cost and suitable for relatively large springs

The Neyoro G, the Paliney 6 and the Paliney 7 materials, which are madeby Ney Metal Co, and which are also good spring candidates.

However, for very thin springs, Tungsten is preferable, mainly to takeadvantage of its higher strength. In other applications, springs may bemade of aluminum, copper, or they can be wire-bonded directly to thecomponents.

Still More Embodiments

FIG. 18 shows a socket with springs that have a shape called “3-VEES”.This spring shape reduces the amount of wiping action. This effect maybe desirable in certain kinds of applications.

FIG. 19 shows other shapes of springs that can be used for variousapplications. They all can be “parallel nested”. They are called“3-Cees”, the “3-Vees” Symmetric, ”, the “3-Vees” Asymmetric and the“2-Vees” respectively.

All these springs still behave and have their force-deflection curves asa formed beam, not as a straight column. And also their shape obviouslyallows parallel nesting.

Spring Design Trade-Offs for Parallel Nesting

If we compare the springs in the previous figures, their shape ingeneral and specifically the shape of their “bellies” can be optimizedfor pitch, spring compression and wiping action. FIG. 20 shows a numberof C-shaped springs. Their bellies are arcs or segments of circles, withvarying amounts of protrusion. We can identify the shape by the includedangle “X” shown in spring B. (See “DEFINITIONS”). In this case, thisangle X equals the nesting angle.

For clarity, the springs shown in FIG. 20 were drawn with a wirediameter of 0.200″ (approx. 5.080 mm). The radius of the circle is1.000″ (approx. 2.540 mm). The angle “X” is varied from 90 to 30degrees. Two similar springs are placed next to each other in order todetermine how small a “pitch” we can achieve with each pair of springs.

Nesting Angle [NA]

The “best geometry” of parallel nested springs is achieved when thesprings have the desired spring force/deflection characteristics and atthe same time, the smallest pitch and the proper allowance fornon-planarity. It is a trade-off. In general, the nesting angle shouldbe equal to or less than 60 degrees. An angle of 45 could be a goodtrade-off between spring characteristics and pitch. An angle of 30degrees increases the stiffness of the springs, but reduces the pitcheven more yet. The same conclusion applies to other shapes including theChevron or the 3-Vees springs, etc.

In general, a smaller nesting angle would give us a smaller pitch, butwould make the springs stiffer. We can compensate for that by making thespring longer or making the belly of the spring deeper, so as to makethe spring softer and still keeping the small pitch.

Visual/Perceptual Interference

FIG. 21 shows the top view of a typical socket. It shows the top comb,with the holes through which the springs protrude. In this specificexample, the center distance is 0.020″ (approx. 0.508 mm) in both the x-and the y-directions. Above the top comb is a locating plate with a“window” or “nest”, which would receive the Device under Test. The nesthere is shown as a 0.500″ (approx. 12.70 mm) square opening. Thedimensions shown here are arbitrary, selected simply to illustrate theconcepts.

FIG. 22 shows a detailed close-up view of FIG. 21. Shown are springsnear the bottom left-hand corner of the top comb and the springsunderneath it. It also shows the footprints of the springs under thecomb, as if the comb is transparent. The dark, full circles are theupper “tips” of the springs. The crosshatched circles are cross-sectionof the “bellies” of the springs underneath the comb.

Highlighted are two springs “A” and “B”. It is obvious that the belliesand bodies of the springs look as if they overlap and interfere witheach other, but in reality, we do know now that they are parallelnested. Hence, no problem.

We can also notice that each row of springs is completely independentfrom the adjacent rows.

Reducing the Pitch by Approximately 30%

FIG. 24 shows the matrix with its 0.020″×0.020″ (approx. 0.508×0.508 mm)pitch. The centerlines of the rows and columns are orthogonal and areeither horizontal or vertical. The bellies of the springs are along thesame directions of the centerlines. Refer also to FIGS. 21 and 22. Inthis case, the bellies are along the horizontal axis. At the right-handside of the figure we show the same set of springs, but arranged alongcenterlines that are at 45 degrees diagonal to the previous arrangement.The pitch between the springs now has been reduced from 0.020″ (approx.0.508 mm) to approx 0.014″ (approx. 0.356 mm). This is approximately a30% reduction in pitch. FIG. 23 shows a close-up view of FIG. 24.

Please note that the pitch of 0.020″×0.020″ was selected simply toillustrate the method, by using a pitch size that is easy for thecalculations. Similar results will occur if we select any other pitch.Also, the present invention is geared for small pitches, down to half orquarter the one used in this example, and even smaller yet.

Bundling or Encapsulation

For ease of manufacturing and assembly, the springs can be pre-assembledinto a block as shown in FIG. 25. For clarity, the springs are shownhere farther apart than they would be in an actual application. A single“slab” can be combined with other slabs into blocks for ease ofassembly. In an application where the pitch is relatively large withrespect to the spring wire diameters, we can go directly to the blockform, bypassing the use of individual slabs.

The material used to “bundle” the springs as shown can be a very softelastomeric material, or a gel, or even very fluffy foam. It is simply away to keep the springs together until they are installed in place intotheir socket housing. We do not rely on the encapsulant to provide or toapply any appreciable force, if any, during the operation of the socket.

FIG. 26 shows another alternative with the encapsulant in three distinctparts. The two gaps between the three different parts would help in themanufacturing process. They allow us to use “spacers” and otherfixturing means during the manufacturing or assembly operation. Theencapsulation can serve an additional purpose, which is to act as aconductive shield or ground, as will be explained later.

Alternatively, we could use a “wax” as the encapsulating material. Then,after the springs are fully assembled inside the housing, we could meltthe wax and remove it. This would be similar to the “lost wax” processused in certain operations in the industry, like in “investmentcasting”.

APPLICATION EXAMPLE 3

FIG. 27 shows another example of a socket as per this invention. Here,the springs are fixed somewhere close to the center of the socket by aholding means. The portions of the springs above and below the holdingmeans are shaped as Chevron springs in this case. Each portion above theholding means flexes independently from the portion below the holdingmeans.

We can retain the springs in the holding means by a number of methods.We can insert mold the springs in the holding means. We can do that forone slab at a time and then stack the slabs together, or insert moldthem as one block in one shot. Similar to the encapsulation method.

We can also mold the holding means into individual slabs, withappropriate groves in each slab, and then snap the individual spring inits respective grove. This would also allow us to populate the slabseither fully or at specific spots, for a specific reason. Basically, itis so that the springs locations would match the locations of thecontact pads of the DUT.

We could also insert the springs into slabs with groves or force thesprings into blank slabs, almost like a flat sheet of plastic, by theuse of ultrasonic means or the like. See FIGS. 41 through 45 for slabswith groves.

We could also make the slabs to have two layers of springs, one layer oneach of the two faces, and then stack them next to each other, placingsome spacers between them to ensure that the pitch between the springsis as needed.

Insert Molding

Encapsulation may not be needed to hold the springs together if we usethe insert molding process.

FIG. 27 shows that the springs will be attached at one point to theholding means and the opposite ends of the springs are free to protrudethrough the respective combs, as shown. In this figure, we also noticethat the portions of the springs below and above the carrier are notequal in length. We may use such different length springs if the matingdevices at the top and bottom of the socket have varying amounts ofnon-planarity. Each length of spring accommodates different amounts ofnon-planarity and applies different amounts of force.

In this case, the molded holding means is fixed to the housing and thesprings on each side of the carrier act independently from each other. Aslider can be used to retract the top portion of the springs, ifdesired.

Mounting of Socket to Substrates

Sockets may be soldered to the board by adding solder tails to thesprings inserted in through holes in the printed circuit board or may besurface mounted.

APPLICATION EXAMPLE 4

FIG. 28 shows another socket according to the present invention, wherethe springs have solder tails.

APPLICATION EXAMPLE 5

FIG. 29 shows yet another version of the socket according to the presentinvention, where the springs are ending in “J-leads”, or the like, to besurface mounted to the PCB.

APPLICATION EXAMPLE 6

In most of the above examples, the DUT would be placed in a nest, tohold it on top of the springs, and in registration with the springstips.

The DUT can be a BGA, a substrate, a chip or the like. Most of thesedevices are controlled by Industry Standards. JEDEC for example havestandards for BGAs. FIGS. 30 and 31 show a BGA sitting in a nest on topof the springs tips. The nest is also shown. Here, the nest is made outof two parts, which we could call jaws. One jaw is “fixed”, while theother slides out and in, to allow the package to be inserted and then beclamped in place.

To enhance the registration and to minimize the effect of tolerancebuild-up, it is recommended to use the fixed jaw of the nest as the“datum”, and to place the BGA such that the datum of the BGA wouldcoincide with that of the nest. According to JEDEC, this would orientthe BGA to be positioned as shown in FIG. 31. In this case, the “A1Corner” of the BGA should be at the bottom left corner, as shown.

Insulation, Shielding and Impedance Control

All the springs can be individually insulated by using a thin coverlayer of plastic. It is possible to shield and ground the contacts bycoating the springs with a conductive layer on top of the insulatinglayer. This would create an electrical conductor similar to a “coaxcable”.

The insulation can be achieved by a number of different ways. Forexample, the portions of the springs that need to be renderednon-conductive can be oxidized chemically or by any other means to makethem non-conductive. Similarly, the conductive layer can be applied overthe insulation by either Electroless nickel plating, or by vapordeposition, by plasma, or any other suitable method. Also thisconductive layer could be selectively concentrated more along themechanical neutral axis of the springs, where the deflection is minimal,to minimize cracking of the layer due to the bending and flexing of thesprings.

Another alternative is to have an encapsulant surround a number ofsprings, or all of the springs, where the encapsulating material can be“conductive”. The encapsulation can then be “grounded”. This wouldprovide “electrical shielding” from stray electrical signals and noise,and the springs would then behave as shielded “coax cables”, and wouldhave a “controlled impedance”.

We can take advantage of the geometry of the springs and the way theyare mounted in their housing, to improve their electrical performance.The springs are arranged in rows and are “in-line” and have a gap orspace between each line and row of springs. We can provide a layer orsheet of conductive material, placed between the rows of springs. Thiscan act as a shield or ground layer to electrically isolate each row.Effectively, we would have a situation almost similar to “micro-strips”.If the individual springs are insulated, then the ground layer/sheet canbe a simple thin sheet of metal, or a number of wires or a mesh, or evena layer of conductive plastic, connected to an appropriate ground point.If the individual springs were not insulated, then the ground planewould be insulated on any side that faces such springs.

If the application requires additional shielding, we can use some of thesprings to act as a ground. In other words, we would have one spring forsignal and the adjacent spring for ground, etc. This can duplicate theeffect of the ground plane mentioned above. Furthermore, we can use thisscheme together with the ground plane, to really surround the “live”spring with a tight cage of ground. A conductive encapsulant can do thesame shielding.

Retractable Springs (or “Turtle Socket”)

FIG. 32 shows a socket with “retractable” springs, so that the springswould be protected from damage while the socket is open. Special meansretract the springs so that they hide inside the envelope of thehousing, under the surface of the comb.

The test socket in this example uses a cam that retracts the tips of thespring inwards, inside the housing, when the lid is opened.

FIG. 33 shows a close-up view with cross-section of this test socket.The cam actuates a “connecting rod”, which pushes the “slider”,

When the lid is at any position, roughly between positions A and C, (seeFIG. 32 for a full picture of all the Positions, A through E), the camis at its “high” dwell. It pushes the connecting rod a certain distance,to push on the belly of each spring, enough to get the tips of thesprings inside the housing and beneath the outside surfaces of thecombs. In this position, the springs are fully protected from anyoutside interference. Any object can be placed on top of the comb, i.e.in the nest, without touching, disturbing or damaging the springs. Thiscondition will prevail until the lid is rotated from position A toapprox. position C of FIG. 32.

FIG. 34 shows the lid in position D, i.e. at roughly 30 degrees. Herethe cam is now off its high dwell and is not pushing the connecting rod.The springs are in their “no-load” or free shape, where they have pushedthe slider back, so that they are now at their fully extended length.The spring tips are now out of the housing and they will start tocontact the device under test.

FIG. 35 shows the lid fully closed. The cam is even at a lower dwellpoint and there is a gap between the cam and the connecting rod. Theconnecting rod is not pushing against the slider and the slider is freeto move to wherever the springs want it to go. The springs will findtheir best position under compression.

In a typical application, where test sockets are used in Automatic TestEquipment (ATE), there are alternate ways to protect the springs. Forexample, the connecting rod or the slider can be pushed directly by theATE machine.

A spring-loaded comb that lifts up and protects the springs may also beused. In its rest condition, the comb is raised above the level of thesprings' tips, so that the springs are hidden underneath.

Yet Another Embodiment

FIG. 37 shows a socket made of modular slabs, which are contained insidea “cage”. FIG. 36 shows an alternative to the slab shown in FIG. 37. Thecage in FIG. 37 is made of skeletal members, in a way so as to haveaccess openings on all sides and both at the top and bottom halves ofthe socket. This way, we can reach inside the cage from the outside withopen combs, and guide the tips of the springs into their respectiveapertures in the socket combs. Using two sets of such open combs, whichwe would call the “threading combs”, we would get in from one direction,say the X-direction, and push the individual fingers of one threadingcomb between each pair of adjacent springs. Then we would get the secondthreading comb and push its fingers in the perpendicular direction, inthis case the Y-direction, and again insert each finger of the combbetween each pair of adjacent tips of springs. This will trap eachspring tip between two pairs of threading comb fingers, each pair beingperpendicular to the other. This would hold the spring tips firmly inposition. Then we would bring all these open combs with the springstrapped between them towards the socket comb, which we will callinterchangeably “connector comb” also, and push the springs home.

FIG. 37 does not show the springs. This is just for clarity. Only onespring is shown, going through an aperture of the socket comb. Even thesocket comb is shown as a thin section, so as not to hide the details ofthe modular construction.

FIGS. 38, 39 and 40 show three orthogonal views of the socket of FIG.37.

FIGS. 41 through 44 show details of the slab, and some dimensions. Inthis example, the center distance between the springs is 0.009″. Alsothe slab here is what I call a double slab. It has springs on bothsides. The total thickness of the slab is 0.018″. So, when several slabsare placed next to each other, to create a “stack”, the whole matrix ofsprings will automatically be on 0.009″ center or pitch.

FIG. 45 shows two alternate ways to make another double slab, withsprings on both sides, on alternating pitch distribution. However, herethe springs are every other space, which results in that the springs areon 0.018″ center. However, if we look at the matrix, tilted at 45degrees, the resulting matrix would have a center distance of only0.0127″.

All the above is to facilitate the manufacturing processes to make suchsockets and connectors. FIGS. 46 and 47 show details of how to securethe socket combs to the housing and how to register the housing to thetest board, using some locating dowel pins.

(Section 2—Probes)

Probes Applications

Now I will use many of the parts of this invention, that were discussedearlier, and apply them to yet another group of products that arereferred to as “Probes”.

Background for Probes

The majority of Probe Cards are built so that they can make contact andtest one chip at a time. The reason is the construction style of theprobes and the fact that the contact pads on chips nowadays are usuallysmall and located at close proximity to each other and that many of thechips have quite a few contact pads that need to be probed. The contactsprings or needles are usually mounted on a printed circuit board (PCB),which is called the probe card. The needles fan out, from the chip as acenter, to the outside, to create a sort of a radial array. The probecard PCB is usually parallel to the chip and the needles are usually ina general direction that is also parallel to the board or the chip. Theneedles act usually as cantilever beams. This general arrangementusually requires a considerably large amount of area (footprint) that isparallel to the board and to the chip, and it is the main reason thatonly a limited number of needles can be accommodated on the probe card.

Because of all that, most of the times, the probe card is mechanicallypositioned, so that the spring tips touch the contact pads on the chipand then the chip is tested electrically. After the chip is tested, theprobe card is “indexed”; i.e. repositioned, mechanically, to contact thenext chip and then the electrical test is repeated. Actually in manycases, the wafer is indexed while the probe card is held in place.

It is time consuming to test the chips this way, i.e. to test each chipindividually, because the wafer has to be repositioned mechanically foreach chip. It would be nicer if it were possible to contact more thanone chip with one mechanical setting of the probe card. In such a case,the electrical test would be done on a first chip, then without anyfurther mechanical repositioning, the second chip would be testedelectrically, then the third, etc. until all the chips that arecontacted by the probe card are tested electrically.

So, it is more desirable to test a number of chips with one mechanicalsetting. Better yet, it would be more economical, if a whole wafer couldbe contacted, with one mechanical setting. Recently, attempts have beenmade to test a whole wafer, or a large portion of same, i.e. more thanone chip, at one time. “FormFactor, Inc., Livermore, Calif.” has shownin their various patents, a number of ways to accomplish some of that.However, those methods have their advantages but also some limitations.The proposed approach could be fairly expensive. But the important thingthat I notice particularly, is that it lacks a specific feature, namelythe comb, which is part of this present invention here.

According to the designs in this invention, a whole group of chips or awhole wafer can be contacted at one time. This can be accomplished byusing the Form Factor approach and combining it with my comb. Othermethods will also be presented that use totally different approaches.

Furthermore, since many of these tests are frequently done at varyingtemperatures, the effects of TCE Mismatch can ruin such tests and/ordamage the chips. The designs in this invention take care of thisproblem as well.

On a different front, packages and Printed Circuit Boards (PCBs) andsubstrates also get tested frequently. Packages can be tested using“Test Sockets”, but PCBs and substrates are not amenable to this methodof testing. So, PCBs and substrates could be tested using probes, ifnecessary. They could also be tested using the “Test Heads” mentionedearlier.

Another problem with most present types of probes is that the needles,being long extended cantilevers, are pretty delicate and prone to bebent out of shape and out of position, if they are not handled verycarefully.

I will describe in this section the designs of the probes and probecards, as per the present invention. They aim to solve all the aboveshortcoming of probes and probe cards presently on the market.

Details of the Proposed Solutions

FIGS. 48 and 49 show isometric views of an example of a “probe” that canbe built according to the present invention. FIG. 48 shows the probe,looking down at it from above, and FIG. 49, looking up at it from below.

I will describe the major steps required to build such a probe.

Application of the Concepts to “Probes”

Next, I will show one example of how to apply the above concepts to makea “PROBE”, using the “Chevron” springs/needles. The same can be donewith other shapes of springs or needles, like those I described earlier,or like those that will be shown later.

Also notice that the number of springs placed in any one row is optionaland the number of rows or stacks or slabs is also optional.

Then, I will talk about other examples including one, where the productcan be used as a test socket as well.

First Example of a Probe

I will first show a probe, with a 20 by 20 matrix of Chevron springs orneedles. I will then show in the subsequent figures how we can put sucha probe together and then later I will show some details of individualcomponents of such a probe.

Please note that the parts shown in FIGS. 50 through 55 are shown as ifthey are laid flat on a table, as during the manufacturing/assemblyprocess. After the assembly is completed, the probe will most probablybe used in a vertical position, as shown in FIGS. 48 & 49.

FIGS. 48 & 49 show a probe containing a matrix of 20 by 20 Chevronneedles, arranged on 0.020″ pitch. The needles are obviously in a“parallel nesting” arrangement.

Please notice that I have used 0.020″ pitch here just for illustration.It makes is easier to see the details. The same concepts and principlesapply to smaller center distances. We are actually working right now ona model that will have a center distance of 50 micron, i.e. approx.0.002″.

Notice also that the tips of the needles are located within holes of a“comb”. This comb locates the needles accurately and in alignment, sothat they match the location of corresponding contact pads on the chipor wafer under test, and at the same time, protects the needles fromdamage.

In addition, the comb can be made of a material that has a ThermalCoefficient of Expansion that matches that of the Device Under Test(DUT). This way, when the tests are done under varying temperatures, thespring tips will remain in their respective position relative to theDUT.

FIG. 50 shows the start of the basic “building block” of the aboveprobe. This is what I call the “SLAB”. The figure shows the primarycomponents of such a slab. Basically, they include the needles and thesupport member. The latter can be a PCB, or it can be a plate togetherwith a flex circuit, or any equivalent arrangement. Notice severalthings here.

First, the needles are slightly different from the one shown earlier.Here each spring has three major portions. See also FIG. 63. The firstis a “flexible body” or “flex portion”, similar to the needles shownearlier. The second is the spring “tip”, which would go through thecomb, again similar to the one shown earlier. The third portion is thenew thing. It is the “anchor”. It is the part that holds the spring tothe support member. In particular, the anchor has a “kink” or similarfeature somewhere along its length, where it will lay against thesupport member. The anchor is not the “flexing” part of the spring. Itspecifically provides what I call the “anchoring and orientation”feature. It first holds the spring in position, and second it keeps its“orientation” with respect to the support member and to the otherneedles. In other words, it prevents it from rotating out of place.

Second, the top end of the spring will eventually be soldered to itsrespective contact pad on the support member, as in FIG. 51.

Third, a certain length of the spring, between the tip and the solderend, can be insulated. This would prevent any “short circuit”, if everany two adjacent needles do touch.

Fourth, a certain length of that insulated portion of the spring canhave a conductive material layer over the insulation, where the latterlayer could be “grounded”, so that the whole thing would act as agrounded coax cable, to improve the electrical performance of the probe.

Fifth, the support member can be a stiff board made like a PCB or ametal plate together with a “flex circuit on it, or any equivalentarrangement. The solder pads will be staggered and spread over a numberof rows to accommodate the number of needles that will be on smallcenter distances. This could be similar to present probe cards.

FIG. 52 shows some of the steps to affix the needle to the support. Thelower edge of the support will be the “anchor” for the needles.

FIG. 53 shows a “slab” after going through some of the subsequentassembly steps, where more needles are mounted on the support member andsoldered to their corresponding pads. If the needles are insulated andcovered/shielded by a conductive material, then they will also be“glued” to the support member and their shields “grounded”. Spacersand/or fillers will be added, as necessary, to create slabs of uniformthickness.

FIG. 54 shows a “STACK” of 20 slabs, assembled together to make thebasic probe. Each slab is made as the one shown earlier. The stack shownhere would be used together with a comb or two, as will be explainedlater, to end up like the one shown in FIG. 55. The whole thing willthen be “fixtured” properly, to work with whatever testing equipmentthat are used for the probing operation. It will then look as show inFIGS. 48 and 49.

Frequently, the chip/DUT does not have a full matrix of contact pads.The pads may be on the perimeter; and even so, they may not be evenlydistributed all on the same pitch; or some gaps may exist between somecontact pads. In such cases, only the proper number of needles would beselectively mounted on the various slabs, so that after all the slabsare stacked together, the needles will be distributed in a pattern thatmatches the pattern of the contact pads of the DUT. This will create asort of a “matched set”.

Next, I will show some details of the major components of the probestack. FIG. 56 shows a side view of the stack together with a comb,looking at it from the front. FIG. 57 is looking at it from the back.Notice here that there is only one comb, so we would get wipe or scrub.Compare this with FIG. 59.

FIG. 58 shows an enlarged partial cross-sectional view of the comb andthe tips of the probe needles. The holes in the comb are tapered both atthe top and bottom of the comb. This gives them an hourglass shape,which would allow the needles to tilt and sway sideways, if deflectedunder compression. This tilting action would result in the “wipe” or“scrub”, which is desirable in most cases.

FIG. 59 shows a similar view, but with two such combs. It is clear thatthe two combs, acting rigidly together, would “guide” the needles andprevent them from swaying. Hence, in this case, we would not get anyappreciable scrub, if at all. I will expand on this later.

Please note that if desired, the two combs could be mounted such thatthey may slide sideways with respect to each other, in which case wewould get scrub. We can go one step further. By allowing the two combsto slide only a certain distance with respect to each other, we cancontrol how much scrub we would get. So, we can decide on the amount ofscrub, doing this kind of “gymnastics”. This is another way to controlthe scrub, as compared to the methods mentioned earlier, when I proposedto use the shape of the spring and the amount of symmetry, etc. tocontrol the amount of scrub. Another method is to have two combs, whereone would have a hole and the other a slot.

Notice also that the comb can be made of several layers, where the holesin the different layers can have successively larger diameters, tosimulate the hourglass shape. This can make the manufacturing processeasier. However, these layers will still behave as if there is only onecomb in the system, like a “glue-lam” beam, and we would still get thedesired wipe/scrub.

Similarly, if the diameter of the hole is very small compared to itslength, i.e. the thickness of the comb, then it would be very difficultand/or expensive to make such a hole. By using two or more layers tomake the comb, the length of the hole in each individual layer will beshorter and the aspect ratio of the hole will be more favorable, thuseasier and less expensive to make.

Other Examples of Probes

In all the previous FIGS. 48 through 57, the way to get the signals outfrom the contact springs and to route them to the outside world wasthrough the top of the support member. In those figures I had used aflex circuit as the conduit. The two ends at the right and left of thetop portion of the support member are where the signals would go out at.The basic support member can be a sheet metal or the like, and it willcarry the flex circuit.

An alternate way is shown in FIG. 60. Here we make the whole supportmember out of a PCB material, with its own traces and edge board contactpads. Then we can use edge board connectors to get the signals out tothe outside world.

FIG. 61 shows yet another alternative to get the signals out. Here theconnections can be directed to the top of the support member. This wouldmake the whole probe narrower, and it would have a smaller footprint ontop of the DUT.

FIG. 62 demonstrates how we can mount the contact springs selectively,so as to match the pattern of the contact pads of the DUT.

“Vertical” Needles with “Offset”: Cantilever Needles

FIG. 63 shows six needles. Spring #1 is the one shown earlier, in FIGS.48 through 57.

Needles #2 and #3 are variations of #1. Notice that all these threeneedles have their tips “in line” with their anchors, i.e. verticallyunderneath it. In other words, their axis is vertical. Notice also how aportion of their body lays outside the axis, making it easier for axialforces to bend the springs. Such needles could be used if we have acondition as shown in FIGS. 64 and 65.

FIG. 64 shows the axes of the springs on an increasingly larger angle tothe vertical, as the support members/carriers are farther away from thecenter. FIG. 65 shows another alternative, where the springs are slopingin both the X- and the Y-directions.

Needles #4 through #6 are basically very similar to their counterparts#1 through #3, except for one special feature. The tips are “offset”sideways, away from the vertical line. One main advantage of thisconfiguration is to accommodate the situation shown in FIGS. 2, 66 and67, FIGS. 69 through 79, 82 through 85 and 87 through 101. The anchorsof the needles will be on the outside of the chip pattern, while thetips of the needles will be extending farther inwards, to create atighter pattern, to match that of the chip. Furthermore, the needles canbe tapered, i.e. with the tip diameter smaller than the diameter at theanchor. The tapering can be gradual or in steps. The amount of offsetand its effect on the force-deflection relation and on the amount ofwipe/scrub will have to be taken into consideration during the design ofthe needles.

For our purposes here, we will consider the axis of these offset springsto be the line between the anchor point and the lower tip of the spring.See FIG. 2 and DEFINITIONS. You will notice also that in all theseoffset springs, a portion of the flex portion of the spring body iseccentrically offset away from the spring axis, similar to the springs#1 through 3.

Also, for ease of referencing, I will call most of these offset springs“CANTILEVER” springs.

Probe for a Row of Chips

FIG. 66 shows a “row” of probe entities or “cells”, which is what can bedone if we want to test more than one chip at a time and if the contactpads on the DUT are extremely close to each other. This would be done ifthe thinnest support members may still be too large and could not matchthe center distances of the DUT. In this case, we can make a “row” ofprobe “cells”, each cell matching the DUT, but with a “gap” betweensubsequent cells, to accommodate the size of the support members. Inuse, we would test one “set” of chips, then “index” to test the chips inthe “gaps”. Then we can index to the adjacent row of chips and so on.

Probe for a Cluster of Chips

FIG. 67 shows a “cluster” of probe entities or cells, which is what canbe done if we want to test even more than one row of chips at a time. Inthis case, we would need to “index” in both the X- and the Y-directions,to ensure that we test all the chips under the cluster footprint. Then,we would again, index to the next adjacent cluster footprint and so on.

“Connector Box” as a Probe

If we visualize that the springs or needles described above are enclosedin some “housing”. They would basically become a “connector box” or a“socket”, or a “test head” or a “test module”.

Now, let us visualize that we would place a PCB on top of the connectorand place all this, above the chip or the wafer. Place all this betweentwo pressure plates, and bingo, we have a new way to probe wafers. Thesprings or needles inside the connector box can be arranged as a fullmatrix; or placed in only the desired locations, to create another“matched” set of prober and wafer, similar to what was mentionedearlier.

There are two potential problems with this kind of arrangement, althoughthey are not insurmountable. First, the top PCB, which will contact thesprings or needles at the top of the connector box, would need to havecontact pads that are as small as those of the DUT and distributed onsimilar distances, etc. The other thing would be the “routing” of thesignals out to the outside word. One solution that I can visualize wouldbe to use a pretty thick “multi-layer” board, with all the fine featuresin it. A second solution is to have a “matching wafer” kind of device toact as the top PCB. A third solution is to tie the needles to thematching wafer, like by wire-bonding. This gets to look a lot like someof the devices developed by “FormFactor”, References 2 and 3, but withsome novel variations.

FIG. 68 shows still another application of the concepts of thisinvention. Here, the springs are joined directly onto a “basesubstrate”. They can be soldered, brazed, wire-bonded, or joined by anyother suitable means. They can also be “grown” (created) on location.(See “FormFactor”, Refs 1 & 2). The other “free” ends of the springsprotrude through a comb, similar to the combs described earlier. Thecomb helps in positioning the springs tips and will create scrub or wipeand will control its magnitude. Notice also the wide funnel entry at thebottom of each hole of the comb. This helps in guiding the springsduring assembly.

Needles, with Basically Perpendicular Axis to DUT

Please notice that all the above needles have their general shape andaxis in a basically “perpendicular” direction to the surface of the DUT.This configuration allows us to pack more needles in comparatively thesame area as the DUT. Some “test heads” or “test modules” have theirsprings axes perpendicular to the DUT. These will be in the category asour devices described earlier. I would like to refer to this wholecategory as “vertical needles” or “probes with vertical needles”.

This is in contrast to most of the probe cards presently on the market

Since the DUT is usually held in a horizontal position, I have earlierreferred to the above springs or needles as “vertical”. I intended it tomean “perpendicular axis” to the DUT.

Needles, with Axis Basically Slanted to DUT, or Cantilever.

We can group these into two sub-groups: One where the springs anchorsare horizontal and parallel to the DUT. We will call them “CantileverHorizontal Probe Cards”. The second sub-group will have the sprigsanchors vertical and we will call them “Cantilever Vertical ProbeCards”.

We can use most of the concepts proposed here for most of the probecards. We would still get a lot of the advantages and benefits obtainedby the concepts proposed here.

Horizontal Cantilever Probe Cards

The needles in the present probe cards are essentially parallel to theDUT, “fanning out” from the DUT as a center, and spreading out toaccommodate being soldered to the card solder pads. These needles havebasically similar components as the ones shown in FIG. 63. I mean, theyhave an anchor, which is attached to the card. They have a “flex body”,which is usually a straight cantilever, and they have a tip which isalmost at 90 degrees to the flex body. The needles are usually made offairly thick spring wires and look and perform almost as straightcantilevers, with their last tips tapered down to very small diametersand points. The tips are usually not protected by anything like ourcombs. They are usually fragile and need to be kept in protective boxesto prevent any accidental damage due to handling etc.

Applying Our Concepts to Horizontal Cantilever Probe Cards

I propose at least two changes to these present probe cards. The firstis to have the needles look more like the ones shown in FIG. 63. Themain difference is that their anchor portions would be horizontal as inFIG. 69, so that they can be mounted the same way they are mounted now.

Notice the kink in the anchor portion of the spring. This is a specialfeature, which controls the orientation of the whole spring body in acertain plane. In this case, it is the horizontal plane and it isperpendicular to the plane of the flex portion of the spring. Their flexbody would look more like one of the springs described earlier, i.e.with a belly, but with a more pronounced slope downwards. [Claim]

The second change is to use a comb to control the tip of the needles andto create and promote and control the “scrub”, again as in FIG. 69. Thecomb can be mounted on three or more posts on the card. The posts can berigid or spring-loaded.

I have made a model of such needles. It is shown in the following FIGS.70 through 77. It is basically a modification of needles Number 4, 5 or6, in FIG. 63. I have actuated it to show how it would work and how muchscrub we can get with such a design and also how we can control thescrub. See next figures.

The same shape needles can be used with the “perpendicular” probe aswell, especially like the one shown in FIGS. 66 and 67.

Visual Model of the “Scrub”

FIGS. 70 through 77 are eight scanned views of a probe needle that canbe used with probe cards. Such needles could be used with either“parallel” or “perpendicular” kind of probe cards.

The views show the needle, with its anchor point at the top left corner.The needle “flex body” then stretches downwards and to the right. At thebottom right corner of the view, we can see two horizontal dark lines.The lower thicker one represents the chip or wafer or any DUT. Thethinner line above it represents the comb. The tip of the needle passesthrough a hole in the comb and then protrudes downwards to meet the DUT.

I have included a background with a grid, to make it easier to observethe deflection of the needle.

FIG. 70 shows the needle, when it has just touched the DUT. No-Load andNo Compression.

FIG. 71 shows the next step. Here the picture simulates the probe cardbeing lowered against the DUT. The probe card and the needle anchorpoint have moved down an increment of 0.025″.

We can see that the needle has been compressed down onto the DUT, thebody of the needle has deflected slightly and the tip has tiltedslightly and the contact point has moved a little bit to the right. Thisis what creates the desirable “scrub”.

FIG. 72 shows the following step. Here the probe card was loweredanother increment of 0.025″. The body of the needle is bent more. Andthe contact point has moved more to the right, creating more scrub.

The following Figures through FIG. 76 show the further progressivedescent of the probe card down towards the DUT.

FIG. 77 shows an interesting point. The probe card has moved down yetanother increment, but the tip of the spring has not moved to the rightanymore. The reason is that the shape of the hole or aperture in thecomb has limited the tilting of the tail of the spring. When the tail ofthe spring tilts so far, that it touches the walls or edges of the hole,then it cannot tilt any farther. We can use this feature to control themagnitude of the scrub or wipe.

The movement of the tip of the needle and of the contact point betweenthe needle and the DUT is exactly the kind of “SCRUB” that we arelooking for. The location of the comb and the whole geometry of theneedle body and the needle tip control the amount of scrub and itsextent on the surface of the DUT.

And we can design all that to suit the individual case and itsrequirements.

FIGS. 78 and 79 show an isometric and a side view of a probe card,utilizing the kind of spring that we saw in FIGS. 69 through 77. I wouldlike to call such a probe card the Probe Card with Horizontally AnchoredCantilever Contact Springs. For short, “Horizontal Cantilever ProbeCard”. It looks very similar to the conventional probe cards availableon the market, except for the fact that it uses the contact springsaccording to this invention and it also uses our comb and limiter.

FIG. 80 shows a comb, as it is configured to mount on the HorizontalCantilever Probe Cards. FIG. 81 shows the same comb, but on top of it isshown a “Limiter”. Please notice the four lines towards the center ofboth the comb and the limiter. These are the apertures for the contactsprings to go through.

FIG. 82 shows a top view or bottom view of the contact springs of thisHorizontal Cantilever Probe Card. You notice how the tips of the springsare located on the square pattern of the contact pads of the DUT. Butthe bodies of the springs fan out to take advantage of the larger spaceavailable as the distance increases away from the center. The secondends of the springs cannot be located along a true circle in such acase. If we want to have all the springs with the same length, to assuremass production and to reduce costs, we need to locate those second endsalong a path, which allows us to have such a uniform distance from the“square” pattern of the contact pads of the DUT. I will call such a paththe “distorted circle”. This will be explained a little better later, inconjunction with FIGS. 91, part A and part B.

FIG. 83 shows a close up view of the center of FIG. 82. FIG. 84 showsstill a closer view to the same. FIG. 85 shows yet a closer look. Herewe see the slots in the comb and the slots in the limiter on top of thefirst set of slots. We see that the slots are inclined at certainangles. We see also that the slope of the slots is not constant.

Actually the slots should best be in line of the body of the contactsprings. FIG. 86 shows that the slots are directed generally toward thecenter of the DUT, but more precisely in the direction of the springsbodies as the springs fan out as seen in FIG. 82.

Controlling the Amount of Wipe or Scrub

The amount of wipe can be controlled by “guiding” or “pivoting” thespring tips, by the shape of the spring and by the use of “combs”.

For example, the chevron style creates wipe, while the 3-Vees willcreate almost no wipe, depending on the geometry of the Vees. Thechevron spring is asymmetric, while the 3-Vees spring is moresymmetrical. Other shapes of springs can be parallel nested and providewipe or scrub, as well.

The shape of the holes in the comb is also important and affects theamount of the wiping action of the pin. Generally, it should have anhourglass shape. The location of the “waist” or “pinch point” of thehourglass has an important effect, too.

If the pinch point is located very near to the end of the spring, i.e.the tip, then the tilting of the tail and the movement of the springwould be internal or inside between the two pinch points of the top andthe bottom combs. In such a case, we see very little side motion outsidethe combs. Hence, hardly any wipe.

However, if the pinch point were more towards the inside of the combs,then the free tips of the spring would move more sideways. This isbecause the pinch point is farther away from the tip. This geometrypromotes wipe.

If we need to increase the amount/length of the wipe, we can place thepinch point further away from the tip of the spring and more toward thecenter of the spring. This will in essence “multiply” the effect of thetilting or rotation of the spring tail and result in more wiping action.It is like the multiplying effect of any arm or lever pivoting about afulcrum point. So, we can say that the pinch point is the fulcrum ofrotation of the tails.

This way, we can control how far the tip of the spring moves sideways toinsure that the spring stays within the area of its intended contactpad. We can also use the “sides” of the hourglass and/or the edges ofthe hole, to limit the side movement of the spring tip.

Limiting the Amount of Wipe or Scrub

Usually, we need to control the magnitude of the wipe or scrub. We don'twant the tip of the spring to wander off the contact pad of the devicebeing contacted. There are several ways to accomplish that.

We can control the length (magnitude) of the wipe by controlling twothings: First is the tilting angle of the spring tail, and Second, thedistance from the pinch point to the contact pad, i.e. the length of the“lever arm”, which is the portion of the tail beyond the pinch point.

We can control the angle by several methods: 1) by the side walls of theaperture/hole in the comb, 2) by the aspect ratio of the hole, 3) byusing combs with two layers and by the effective aspect ratio of thecombined hole, or 4) by using a combination of a comb together with a“limiter”.

Using the sidewalls of the apertures/holes of the comb. If the holes arehourglass shaped, then the tail of the spring would stop tilting anyfurther once the tail portions touch the sloped surfaces of thehourglass or the edge of the hole.

If the holes have a straight cylindrical or trapezoidal shape, then whenthe tail would tilt far enough, the edges of the hole would stop anyfurther tilting. One part of the tail would touch one edge of the holeand the other part of the tail would touch the opposite end of that samehole. Then the tail would not be able to tilt any farther.

The same applies if the comb is composed of two layers. The effectiveshape of the hole would act as a stop to limit the tilting angle of thetail.

The Limiter

We can also provide another member that looks almost like the comb andplace it near the comb, to act as a “limiter”. The limiter can bephysically touching the comb, or can be placed at a certain distancefrom it.

The holes in the limiter can be similar in shape like the holes in thecomb, or can have a different cross-section. And they can have the samesize or different size.

In addition, the holes in either the comb and/or the limiter can beoblong, like slots, if we look at them from the top view. Again, theslots can be the same size or different in size for the comb as comparedto the limiter. The direction of the slots can be such that the axis ofthe slots would be angled toward the geometric center of the package orDUT, or of the pattern of contact pads. Or, the slots axes could beangled to match the direction of deflection of the contact springs. Thislast choice would be preferred especially with Peripheral Probes

TCE and Avoiding Thermal Mismatch

To reduce the effects of thermal cycling, the comb is made of a materialthat has a Thermal Coefficient of Expansion (TCE) that closely matchesthe material next to it. For example, if we are testing a ceramicpackage, the comb next to the package can be made of a similar ceramicmaterial, or out of a material that has a TCE that closely or exactlymatches that of ceramic. Ideally also, the comb should have a “thermalmass”, [CLAIM], as close to that of the device under test. This way,when the device under test heats up and expands, the comb would heat upat the same rate and temperature. Consequently, the spring tips willremain in their respective position relative to the DUT. There would beno relative motion or lateral translation or migration or frettingcorrosion due to the thermal fluctuations.

Similarly, if the socket is mounted to a printed circuit board made ofFR4, the comb next to the PCB could be made from a similar materialmatching the TCE.

This would be very desirable for test and burn-in applications.

Combs can be used in other applications as well to reduce the effects oftemperature on any interconnection device that interfaces withcomponents made of different materials.

Non-Planarity

This is a very important issue and we can talk about it at length. Themain purpose of using springs or needles is to accommodate“Non-Planarity”. I have put together a spreadsheet to study theallowable Non-Planarity, and how it correlates with the pitch and thegeometry of the springs or needles.

This study can take some time to go through. If anyone is interested, Ican send you a copy of the study. For now, I can give you the summary ofthe following example.

This is for the “chevron” needles shown in the first probe example,described above. The needles are made of 0.010″ (0.25 mm) diameter wire,and are approx. 0.900″ (22.86 mm) long. They were placed on a 0.020″(0.5 mm) center distance. The study covers the deflections of the springtips under the various loads of 10 grams, 20 grams, etc. up to 50 grams.

Basically, the study shows that if we have two adjacent contact padsthat are not co-planar, the belly of the spring touching the higher padwould bulge more than the adjacent needles, which would be touching thelower pads. Based on the geometry of the needles and their location, thedifference in height between the pads can be as much as approx. 0.0066″(0.167 mm) before the needles would touch.

Please note that for different needle geometries, the amount ofallowable non-planarity would be different. Please note also that we can“design” the needles in ways that could allow more or lessNon-Planarity, as desired, within reason.

Vertical Cantilever Probe Cards

FIG. 87 is the basis of all vertical cantilever probe cards. Pleasecompare it with FIG. 69. You will see that the only difference is thatthe anchor portion of the contact spring was changed from being in ahorizontal plane to being in a vertical plane.

FIGS. 88 through 90 show a probe card of this category. FIG. 88 shows acentral support member and four segments. Each segment carries a numberof needles, located in a way such that their contact tips would matchthe pattern of the DUT. Each segment can be manufactured, assembled andprepared in advanced separately and stored. When desired, the propersegments can then be mounted on the core support and be used for aspecific DUT. The time to configure a probe for a new DUT would be veryshort. This is very desirable to the industry.

FIG. 89 shows the segments, where one segment has been mounted to thecore, while the other three are ready to be mounted. FIG. 90 shows allthe four segments mounted.

The number of segments is optional. Most of the electronic devices areeither square or rectangular, so four segments seem to be a logicalchoice. But 6 or 8 segments, or any other number would work too.

Minimizing Production Difficulty

FIG. 91 shows two figures. Fig. A shows a square contact pads pattern onthe DUT, while fig. B shows a circular pattern. The needles are fannedout to utilize the larger space at the outer radii. The logical way isto have the needles positioned as in Fig. B, where the “contact” end ofthe needles would be on a “circle” and the angle increments between theneedle uniform in value. The result of such arrangement would be thatthe “anchor” ends of the needles would fall on a “circle” as well,assuming that all the needles are identical in shape and length, whichwould be another logical thing to do. It would be the contour or pathlabeled “3” on the figure. This would make the manufacturing of thesupport member or the segment easy. It is easy to turn a circular objecton a lathe or the like.

Now, if we use the same approach for the square pad pattern in Fig. A,we will need to push the needle out, so that their “contact” ends wouldfall on the square. The result would be that their “anchor” ends wouldbe displaced from their circular contour, curve 1 in the figure. Theywill fall on a new contour, which is curve 2 in the figure. Now, curve 2is not a circle anymore. It is some “flattened circle” curve. This oneis most probably more difficult to accomplish than the real circularcontour, curve 3. For comparison purposes, I have drawn both curves onboth figures. It is easier to see the difference between the two curves.So curve 3 in fig B is identical to curve 1 in fig A. and curve 2 infig. A is identical to curve 4 in fig. B. So, the question or choicewould be to determine what is more economical. Choice 1 would be to makethe needles identical and have a contour that is not a circular shape,hence more expensive. Choice 2 would be to make the contour circular andeconomical to manufacture and then we would need to form each needleindividually to fit and to suit. My choice would be choice #1. Becausethere usually are so many needles, compared with one support member orfour segments thereof. Such a profile can be programmed on a CNC machinereadily and duplicated more economically than to form hundred of needleseach one individually to a different shape.

Preloading

Usually it is desirable to use soft contact springs for sockets and thelike. But this requires that we deflect the springs a considerableamount to reach the desired contact force and pressure. One way toovercome this dilemma is to “preload” the springs.

FIG. 92 shows one method to preload the needles on a probe card. In thefigure we see the comb that is mounted at a fixed distance from theprobe card, which supports the needles. We also a new member, which Icalled “Pre-Loader”. This one is also mounted at a fixed distance fromboth the card and the comb. A point or portion of the needle will reston the preloader. At this position, the needle is already undercompression. The needle will not lift off the preloader unless and untilsome external force acting say on the contact tip will push the needleup. This force has to be larger than the preload already built in theneedle due to the preloader. Such a situation is desirable frequently.

FIGS. 93 through 101 show a model of such a preloader while it is beinglowered on a DUT. The sequence is shown at increments of 0.025″, similarto the sequence shown in FIGS. 70 through 77. Again, we can see thescrub action, and at the same time, we can see how the needle lifts offthe preloader at a point in time.

HIGHLIGHTS OF ADVANTAGES & BENEFITS OF THE INVENTION

The major advantages and benefits of the concepts described in thisapplication are that:

We are helping the Electronics Industry in its efforts towards“miniaturization”, by providing:

-   -   High-density springs or needles that allow testing of        high-density devices. These include high-density packages, BGAs,        Chips and even whole Wafers, as well as high-density PCBs,        substrates or the like.    -   Testing of these devices improves reliability of electronic end        products and lowers their ultimate costs.    -   Electrically “shielding” the springs and needles reduces the ill        effects of stray electrical signals or noise, and allows for        high frequency testing with controlled impedance.    -   Special materials and plated coatings are available to enhance        the springs and probes properties and performance.

The comb is an important element in the whole concept, as you can seefrom all the above.

-   -   The use of “Combs” creates the desirable scrub or wiping action        and controls its magnitude; hence less contact pressure/force        force is required for good electrical connection.    -   The “Combs” also provides close control on the location and        alignment of the springs and needles, at the “working point”,        i.e. the tip of the springs closest to the contact pads of the        DUT. Hence, better and more reliable electrical contact.    -   TCE-Matched combs defeat the TCE Mismatch syndrome and make this        the best kind of probes for “Thermal Cycling Tests” or for        probing under Fluctuation Thermal Conditions.    -   The “Combs” protect the needles against damage due to accidental        handling, especially in the case of Probe Cards. Hence, longer        life and more economical cost of operation.

1. A system for making electrical connection to an electronic device having at least a first and a second contact features, located in a pattern, with a small center distance between said contact features, the system comprising: a) at least one guide plate, being configured to form a comb, having at least a first and a second apertures for attachment to contact springs, said apertures being disposed in a similar pattern as said pattern of said electronic device and with a small center distance between said apertures, being equal in size to the small center distance between said contact features of said electronic device; and b) at least a first contact spring, having a body, said body having a large diameter or girth, and having a first and a second end, and said spring having a first and a second slender, said pushers having a diameter or girth smaller than that of said body, and said pushers having different length, said first pusher being long and having one of its two ends located next to said first end of said body and its second end being free and as the spring toe free end, while said second pusher being shorter than said first pusher and having one of its two ends located next to said second end of said body and its second end being free and as the spring head free end, and c) a second contact spring, similar in shape and features to said first contact spring, and d) said contact springs being placed adjacent to each other, and e) one free end of said first contact spring passing through said first aperture of said comb, and f) one free end of said second contact spring passing through said second aperture of said comb wherein g) said contact springs are arranged in form of a head-to-toe orientation with respect to each other, wherein said short pusher of said second contact spring is adjacent to said long pusher of said first contact spring, and said long pusher of said second contact spring is adjacent to said short pusher of said first contact spring.
 2. The system as set forth in claim 1, wherein said small center distance between said contact features of said electronic device is smaller than the diameter of said springs body, which is the largest feature of said first or second contact springs, and conversely the diameter of said body of said first or second contact springs is larger than said center distance between said contact features of said electronic device.
 3. The system as set forth in claim 1, wherein the different lengths of said long and short pushers are such that when the free ends of the contact springs are aligned with each other, within a certain distance from the top surface of said comb, said body of both said first and second contact springs would not touch each other when placed in said head to toe orientation.
 4. The system as set forth in claim 1, further comprising: additional contact springs, similar to said first or second contact springs, being placed, adjacent to each other and in a similar head to toe orientation, to form one row of contact springs, wherein the center distance between said contact springs is equal in length to said small center distance between said contact features of said electronic device.
 5. The system as set forth in claim 4, further comprising: additional rows of contact springs, similar to said one row, being placed, adjacent to each other and are placed in a similar head to toe orientation, to form one matrix of contact springs, wherein the center distance between said contact springs is equal in length to said small center distance between said contact features of said electronic device.
 6. A system for making electrical connection to an electronic device having at least a first and a second contact features, located in a pattern, with a small center distance between said contact features, the system comprising: a) at least a first contact spring, having a body, said body having a large diameter or girth, and having a first and a second end, and said spring having a first and a second slender pushers, said pushers having a diameter or girth smaller than that of said body, and said pushers having different length, said first pusher being long and having one of its two ends located next to said first end of said body and its second end being free and as the spring toe free end, while said second pusher being shorter than said first pusher and having one of its two ends located next to said second end of said body and its second end being free and as the spring head free end, and b) a second contact spring, similar in shape and features to said first contact spring, and c) said contact springs being placed adjacent to each other, wherein d) said contact springs are arranged in form of a head-to-toe orientation with respect to each other, wherein said short pusher of said second contact spring is adjacent to said long pusher of said first contact spring, and said long pusher of said second contact spring is adjacent to said short pusher of said first contact spring.
 7. The system as set forth in claim 6, wherein said small center distance between said contact features of said electronic device is smaller than the diameter of said springs body, which is the largest feature of said first or second contact springs, and conversely the diameter of said body of said first or second contact springs is larger than said center distance between said contact features of said electronic device.
 8. The system as set forth in claim 6, wherein the different lengths of said long and short pushers are such that when the free ends of the contact springs are aligned with each other, within a certain distance from the top surface of said comb, said body of both said first and second contact springs would not touch each other when placed in said head to toe orientation.
 9. The system as set forth in claim 6, further comprising: additional contact springs, similar to said first or second contact springs, being placed, adjacent to each other and in a similar head to toe orientation, to form one row of contact springs, wherein the center distance between said contact springs is equal in length to said small center distance between said contact features of said electronic device.
 10. The system as set forth in claim 9, further comprising: additional rows of contact springs, similar to said one row, being placed, adjacent to each other and are placed in a similar head to toe orientation, to form one matrix of contact springs, wherein the center distance between said contact springs is equal in length to said small center distance between said contact features of said electronic device.
 11. A system for making electrical connection to an electronic device having at least a first and a second contact features, located in a pattern, with a small center distance between said contact features, the system comprising: a) at least one guide plate, being configured to form a comb, having at least a first and a second apertures for attachment to contact springs, said apertures being disposed in a similar pattern as said pattern of said electronic device and with a small center distance between said apertures, being equal in size to the small center distance between said contact features of said electronic device; and b) at least a first contact spring, having a body, said body having a large diameter or girth, and having a first and a second end, and said spring having a first and a second slender pushers, said pushers having a diameter or girth smaller than that of said body, and said pushers having different length, said first pusher being long and having one of its two ends located next to said first end of said body and its second end being free and as the spring toe free end, while said second pusher being shorter than said first pusher and having one of its two ends located next to said second end of said body and its second end being free and as the spring head free end, and c) a second contact spring, similar in shape and features to said first contact spring, and d) said contact springs being placed adjacent to each other, and e) one free end of said first contact spring passing through said first aperture of said comb, and making contact with said first contact feature of said electronic device, and f) one free end of said second contact spring passing through said second aperture of said comb and making contact with said second contact feature of said electronic device wherein g) said contact springs are arranged in form of a head-to-toe orientation with respect to each other, wherein said head free end of said first contact spring is adjacent to said toe free end of said second contact spring, and said toe free end of said first contact spring is adjacent to said head free end of said second contact spring.
 12. The system as set forth in claim 11, wherein said small center distance between said contact features of said electronic device is smaller than the diameter of said springs body, which is the largest feature of said first or second contact springs, and conversely the diameter of said body of said first or second contact springs is larger than said center distance between said contact features of said electronic device.
 13. The system as set forth in claim 11, wherein the different lengths of said long and short pushers are such that when the free ends of the contact springs are aligned with each other, within a certain distance from the top surface of said comb, said body of both said first and second contact springs would not touch each other when placed in said head to toe orientation.
 14. The system as set forth in claim 11, further comprising: additional contact springs, similar to said first or second contact springs, being placed, adjacent to each other and in a similar head to toe orientation, to form one row of contact springs, wherein the center distance between said contact springs is equal in length to said small center distance between said contact features of said electronic device.
 15. The system as set forth in claim 14, further comprising: additional rows of contact springs, similar to said one row, being placed, adjacent to each other and are placed in a similar head to toe orientation, to form one matrix of contact springs, wherein the center distance between said contact springs is equal in length to said small center distance between said contact features of said electronic device. 